Recreational and commercial water systems, as well as natural bodies of water, e.g., ponds, are subject to contamination from the presence and growth of microbial species, e.g., algae, pathogenic bacteria and fungi. The sanitizing of standing or recirculating water systems often involves introducing a hypochlorite anion donor material, such as calcium hypochlorite, into the water system to establish therein a desired level, e.g., a sanitizing amount, of free available chlorine (FAC). The introduction of sanitizing amounts of free available chlorine into a water system serves to eradicate or control deleterious amounts of microbial species that are present in the water comprising the water system. Sanitation of water contacted by humans and animals is required because exposure to unsanitized or inadequately sanitized water that contains deleterious amounts of pathogenic bacteria, fungi, viruses, protozoa, etc can lead to the development of infection or disease.
Recreational bodies of water, e.g., swimming pools, hot tubs, spas, etc are generally treated with chlorine-containing sanitizers so as to contain free available chlorine (FAC) in amounts of from 1 to 3 parts FAC per million parts of water [ppm, (sometimes reported as milligrams per Liter, mg/L)]. Water having an FAC content in amounts of greater than 10 ppm (generally in the range of hundreds to thousands of mg/L) can be used to sanitize surfaces or articles to which it is applied, e.g., surfaces of equipment or tables used for the preparation of food. Free available chlorine can be established in an aqueous system by adding regularly a source of hypochlorous acid (HOCl) or hypochlorite anion (ClO−), e.g., calcium hypoochlorite, to the water comprising the aqueous system.
Calcium hypochlorite is a material that is regarded by the transportation industry as being an oxidizer, i.e., a material that can enhance the combustion of organic materials by providing oxygen for combustion. In accordance with U.S. Department of Transportation (DOT) regulations; namely, Title 49, Code of Federal Regulations (CFR), part 173, section 127, paragraph (a), subparagraph (1), [49 CFR §173.127(a)(I)], calcium hypochlorite is categorized as a Division 5.1 oxidizer. More particularly, it is classified as a Packing Group II oxidizer material [49 CFR §172.101 and §173.127(b)(ii)].
The transport of a material categorized as a Division 5.1 oxidizer requires the use of special precautions, which can include the use of special containers. Moreover, materials categorized by the United Nations (specifically the Committee of Experts on the Transportation of Dangerous Goods) or by the US DOT as Division 5.1 oxidizers are generally also classified as oxidizers with reference to storage. See, for example, NFPA (National Fire Protection Association) 430 Code for the Storage of Liquid and Solid Oxidizers. The storage of solid oxidizers can therefore require separate free standing storage facilities and/or special sprinkler systems. Further, the amount of an oxidizer that is permitted to be stored in one location can also be limited. Hence, the requirements for storing and/or shipping calcium hypochlorite (in NFPA oxidizer classes 2 or 3) can involve a substantial cost premium.
It has been proposed to lower the oxidizer classification of calcium hypochlorite by blending certain inorganic water-soluble hydrated materials, such as magnesium sulfate heptahydrate, with the calcium hypochlorite. It has been observed however that when hydrated inorganic water-soluble materials are blended with calcium hypochlorite, the resultant blend is more susceptible to premature decomposition of the calcium hypochlorite during storage.
It would, therefore, be desirable to develop calcium hypochlorite compositions (and formed articles prepared from such compositions) that are not susceptible to premature decomposition during storage, and that are classified as a DOT Packing Group III Division 5.1 oxidizer, more desirably as a DOT non-Division 5.1 oxidizer. It is similarly desirable to have such compositions wherein the storage oxidizer hazard rating, e.g., the NFPA oxidizer class, is reduced. It would also be desirable that such calcium hypochlorite compositions and articles prepared from such compositions have an FAC content that is at least sufficient to allow its practical use in the batch and/or continuous sanitization of water systems, e.g., standing or recirculating water systems, such as a swimming pool, spa, hot tub, cooling tower water, evaporative condenser, etc.